NEW DELHI: Emissions from crop residue burning in neighbouring regions are the major contributor to New Delhi’s notorious winter pollution, a study said. The research, published in the journal Nature Sustainability, shows urban emissions of black carbon from fossil fuel combustion are not always the main contributor to severe air pollution in South Asian megacities like Delhi.
While fossil fuel emissions in Delhi account for 80 per cent of the air pollution plume during the summer, emissions from biomass burning in neighbouring regions rival those from fossil fuels during the fall and winter. “Black carbon aerosols are damaging to human health and their levels are higher in New Delhi than in many other megacities.
During fall and winter, the levels of polluting air particles in New Delhi can reach ten times the limit recommended by the WHO,” said August Andersson, Researcher at the Dept of Environmental Science and Analytical Chemistry, Stockholm University and co-author of the study.
“To determine the environmental effects of black carbon in this highly populated city, it is crucial to quantify the contributions from the key emissions sources.”
The researchers collected air samples from New Delhi during 2011 and analysed their black carbon content to identify the source of the particles. The contribution from biomass burning peaked during dry fall and winter months. In addition, the scientists found that the sources of the high biomass emissions were regional rather than local and urban.
Crop residue burning occurs after harvest, which typically occurs in October/November for wheat, and in April/May for rice. “Our findings contradict the widespread notion that the emission flux between cities and the countryside is mainly one-way,” said Andersson. “The wintertime regional influx of black carbon into New Delhi suggests that to efficiently combat severe air pollution, it is necessary to not only mitigate the urban emissions, but also regional-scale biomass emissions, including agricultural crop residue burning,” he said.